Tensioned flexible covers for reservoirs are illustrated in Gerber U.S. Pat. No. 4,476,992 granted Oct. 16, 1984 and Gerber U.S. Pat. No. 4,446,983 granted May 8, 1984. Both of these flexible covers provide weights which cause rainwater sumps to form at specified locations and tension the horizontal portions of the cover. Water, which is deposited on the surface of the cover in the form of rainfall, drains into the sumps. Some of the reservoir covers have surfaces which cover several acres and the distance traveled by rain falling on the surface may travel up to several hundred feet before dropping into a sump. It may take several hours for the water to travel to a sump. If the temperatures are below freezing, ice may form where the water is particularly slow moving. Such buildup of ice may be a problem to a flexible cover.
Flexible covers which cover large reservoirs and have very large flat areas, are also subject to the deposit of wind blown sand and debris which sometimes collects and weighs down the cover in localized places thereby causing the formation of random depressions which collect rainwater in puddles. These puddles progressively become larger as rainwater accumulates and if the weight of the debris is great enough, the water can be prevented from reaching the sumps. This accumulation of water can be subject to freezing and in some cases can cause distortion of the cover and interfere with the operation of the connecting rainwater sumps.
Another problem which has been noted with flexible reservoir covers which are located in areas subject to occasional high wind velocities is the problem of cover lift-off. Lift-off or cover billowing can occur if air is permitted to enter underneath the cover at the perimeter connection points or through air vents which are normally used to expel air or lighter than air gases trapped beneath the cover. High winds blowing across a reservoir can create negative air pressure above the cover while at the same time it may force air below the cover. Such an adverse condition can cause the cover to lift off the surface and instances of a cover flapping twenty to thirty feet in the air have occurred and damaged the flexible cover.
Finally, flexible covers are custom fitted to cover reservoirs with asymetrical or irregular shapes. It is almost impossible to design tight fitting covers in some of the corners or bays of such reservoirs and some random wrinkling and folding can occur which results in barriers to the free flow of the rainwater toward the sumps and traps wind blown debris. Prior to the present invention, no solution to the above problems has been set forth.